Crackstop structures are formed in dielectric material around an active area of a chip to prevent cracks from propagating into the active area. More specifically, crackstops are placed at the perimeter of chips to prevent propagation of dicing damage to active areas.
For technologies with low-k dielectrics, crackstops are formed as continuous metal walls to act as moisture/oxidation barriers. Continuous metal crackstops, though, can create electrical noise coupling within chips intended for certain RF applications. That is, induced currents in continuous crackstops interfere with RF devices by enabling noise coupling.
To stop this noise coupling, it is possible to make the crackstops discontinuous. Specifically, when the continuous loop is broken, e.g., is discontinuous, signals reaching the ends of the discontinuous crackstops encounter an open circuit termination/impedance discontinuity, reducing noise coupling. However, such structures are incompatible with low-k dielectrics because they allow moisture penetration.